The crisis triggered upheaval in the upper ranks of Britain's police, with Monday's resignation of Assistant Commissioner John Yates — Scotland Yard's top anti-terrorist officer — following that of police chief Paul Stephenson, over their links to an arrested former executive from Murdoch's shuttered News of the World tabloid.

The high-profile resignations are making it harder for Cameron to contain the intensifying scandal on the eve of an unwelcome public grilling by lawmakers for Murdoch and his son James.

The government quickly announced an inquiry into police-media relations and corruption.

Home Secretary Theresa May said that people were naturally asking "who polices the police," and announced an inquiry into "instances of undue influence, inappropriate contractual arrangements and other abuses of power in police relationships with the media and other parties."

Also Monday, Britain's police watchdog said it had received allegations of potential wrongdoing in connection with phone hacking against four senior officers — Stephenson, Yates and two former senior officers. One of the claims is that Yates inappropriately helped get a job for the daughter of former News of the World editor, Neil Wallis.

The Independent Police Complaints Commission said it was looking into the claims.

"I have acted with complete integrity," he said. "My conscience is clear."

Cameron is under heavy pressure after the resignations of Stephenson and Yates, and Sunday's arrest of Murdoch executive Rebekah Brooks — a friend and neighbor whom he has met at least six times since entering office 14 months ago — on suspicion of hacking into the cell phones of celebrities, politicians and others in the news and bribing police for information.

His critics grew louder in London as the prime minister visited South Africa on a two-day visit to the continent already cut short by the crisis

He trimmed another seven hours from his itinerary — having already jettisoned stops in Rwanda and South Sudan — as his government faces a growing number of questions about its cozy relationship with the Murdoch empire during a scandal that has taken down top police and media figures with breathtaking speed and knocked billions off the value of Rupert Murdoch's global media empire.

Parliament was to break for the summer on Tuesday after lawmakers grilled Murdoch, his son James and Brooks, in a highly anticipated public airing about the scandal. Cameron, however, said lawmakers should reconvene Wednesday "so I can make a further statement."

Cameron insisted his Conservative-led government had "taken very decisive action" by setting up a judge-led inquiry into the wrongdoing at the now-defunct Murdoch tabloid News of the World and into the overall relations between British politicians, the media and police.

"We have helped to ensure a large and properly resourced police investigation that can get to the bottom of what happened, and wrongdoing, and we have pretty much demonstrated complete transparency in terms of media contact," Cameron said.

Opposition leader Ed Miliband, however, said Cameron needed to answer "a whole series of questions" about his relationships with Brooks, James Murdoch and Andy Coulson, the former News of the World editor whom Cameron later hired as his communications chief. Coulson resigned from that post in January was arrested earlier this month in the scandal.

"At the moment, he seems unable to provide the leadership the country needs," Miliband said of Cameron.

Rupert Murdoch, too, faces a major test Tuesday in his bid to tame a scandal that has already destroyed the News of the World, cost the jobs of Brooks and Wall Street Journal publisher Les Hinton and sunk the media baron's dream of taking full control of a lucrative satellite broadcaster, British Sky Broadcasting.

At the televised hearing, politicians will seek more details about the scale of criminality at the News of the World. The Murdochs will try to avoid incriminating themselves or doing more harm to their business without misleading Parliament, which is a crime.

The showdown comes as James Murdoch — chairman of BSkyB and chief executive of his father's European and Asian operations — appears increasingly isolated following the departure of Brooks, a possible candidate for arrest or resignation.

News Corp. on Monday appointed commercial lawyer Anthony Grabiner to run its Management and Standards Committee, which will deal with the phone hacking scandal. It said the committee will cooperate with all investigations on hacking and alleged police payments, and carry out its own inquiries.